Variable gain fluidic device



March 17, 1970 M. C. DOHERTY VARIABLE GAIN FLUIDIC DEVICE Filed Feb. 28. 1967 f); V627 to)":

Mart/h GDo/mry United States Patent 3,500,847 VARIABLE GAIN FLUIDIC DEVICE Martin C. Doherty, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Feb. 28, 1967, Ser. No. 619,361 Int. Cl. F15c 1/14, 1/12 US. Cl. 137-815 Claims ABSTRACT OF THE DISCLOSURE A two-dimensional flow fluidic device has two interconnected analog fluid amplifiers of the single receiver type with the power fluid inlets connected to a common source of constant pressurized fluid and first control fluid inlets connected to a source of differentially pressurized fluid input signals to be amplified. Second control fluid inlets coplanar with the first control inlets and power fluid inlets are connected to a common source of pressurized fluid adjustable in pressure to determine the operating point and gain of the fluid amplifiers. A pair of opposed vent passages are located intermediate the receiver and control fluid inlets in each amplifier. The differential pressure of the fluid received in the fluid receivers is the output of the device representing the amplified input signal, and the gain is some value greater or less than unity as determined by the pressure of the fluid supplied to the second control fluid inlets.

My invention relates to fluid amplifier devices, and in particular, to a fluidic device which provides a controllably variable gain function.

The recently developed fluid control devices known as fluid amplifiers (or fluidic devices) having no moving mechanical parts have many advantages over analogous electronic devices. In particular, the fluid amplifier is relatively simple in design, inexpensive in fabrication, capable of withstanding extreme environmental conditions such as shock, vibration, nuclear radiation and high temperature, and the no-rnoving parts feature permits substantially unlimited lifetime thereby achieving long periods of uninterrupted operation. These fluidic devices may be employed as analog and digital computing and control circuit elements, and also as power devices to operate valves and the like. Two broad classes of fluid amplifiers are the analog-type and the digital-type, the subject invention being limited to the analog-type device. The analog fluid amplifier is commonly referred to as the momentum-exchange type wherein a pressurized fluid stream or jet to be controlled, hereinafter described as the power (fluid) jet, is deflected by one or more control fluid jets directed laterally at the power jet from opposite sides thereof. The power jet is normally directed midway between two fluid receivers and is deflected relative to the receivers by an amount proportional to the net sideways momentum of the control jets. This device is therefore commonly described as a proportional or analog device.

The conventional two-receiver analog fluid amplifier is of the constant gain type wherein the gain may be defined as the change in pressure of the fluid received by the receivers corresponding to a predetermined change in the pressure of the fluid supplied to the control fluid inlets. Such conventional constant gain fluid amplifier is a two-dimensional flow device in that the flow paths of the various power and control jets are all coplanar. An example of a variable gain fluid amplifier is described in US. Patent 3,186,422 to W. A. Boothe, in which an additional gain changing control fluid jet provides a deflection of the power jet in a third dimension, that is, in a direction normal to the deflection produced by the first control jets. This latter fluid amplifier is a more complex structure in that it requires an additional control fluid inlet for generating the gain changing control jet and additional fluid receivers.

Therefore, one of the principal objects of my invention is to provide a variable gain fluidic device having a simple structure.

Another object of my invention is to provide a variable gain fluidic device which utilizes only a two dimensional deflection of the power fluid jet to obtain the variable gain feature.

A further object of my invention is to provide such device with a gain which is controllably variable to values greater or less than unity. A similar device, but having a gain controllably variable only to values less than unity, is the subject of a concurrently filed patent application Ser. No. 619,362 to L. R. Kelley, and assigned to the assignee of this application.

Briefly summarized, my invention is a fluidic device including a single fluid amplifier of the analog type when utilizing single-sided input signals or two such fluid amplifiers interconnected for use with push-pull signals. The fluid amplifiers each comprise a power fluid inlet, a single fluid receiver aligned with the centerline axis of the amplifier, and a pair of control fluid inlets disposed in opposing relationship coplanar with the power fluid inlet and receiver for controllably deflecting by momentum exchange the power jet relative to the receiver. A pair of opposed vent passages intermediate the receiver and the control fluid inlets are employed for relieving fluid pressure adjacent the receiver. In the case of the device utilizing double-sided (push-pull) input signals, the power fluid inlets are in communication with a common source of constant pressurized fluid to thereby generate constant pressurized power jets of the fluid. The first of each pair of the control fluid inlets are in communication with a source of variable and differentially pressurized fluid representing a push-pull input signal to be amplified. The second of the control fluid inlets are in communication with a comon source of fluid adjustable in pressure within a predetermined range of pressures and representing a bias signal which determines the operating point on the nonlinear input-output characteristic curve of the fluid amplifier. The gain of my two-dimensional flow device is a function of the bias signal and is controllably variable to values greater or less than unity by adjustment of the pressure thereof.

The features of my invention which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing wherein:

FIGURE 1 is a diagrammatic representation of a pushpull embodiment of the variable gain fluidic device constructed in accordance with my invention;

FIGURE 2 is a schematic representation of the device illustrated in FIGURE 1;

FIGURE 3 is a graphical representation of the nonlinear input-output characteristics for a single-receiver analog fluid amplifier of the type employed in the device of FIGURE 1 for various load conditions; and

FIGURE 4 is a graphical representation of the variable gain characteristics for the variable gain fluidic device of FIGURE 1 at various bias pressures for small signal operation.

Referring now in particular to FIGURE 1, there is shown a variable gain fluidic device constructed in accordance with my invention. The device, as illustrated, consists of two interconnected fluid amplifiers of the analog type, also described as single receiver amplifiers, which are adapted for use with a differentially pressurized (push-pull) input fluid signal to provide at the outputs thereof a corresponding amplified push-pull output signal. The device may also be employed with a single-sided input signal to provide an amplified single-sided output signal but in the latter case it is more economical to construct the device from only one of the fluid amplifiers, that is, to employ only one half of the device of FIG- URE 1. The two fluid amplifiers are illustrated as a whole by numerals 5 and 6 and details of the structure and operation of similar analog-type fluid amplifiers, and their external connections, are provided in US. Patents 3,233,622 and 3,260,456 to W. A. Boothe, whereas, the particular fluid amplifier is disclosed in a copending U.S. patent application Ser. No. 499,403 to W. A. Boothe et al., filed Oct. 21, 1965, and assigned to the same assignee as the present invention. It will suflice to describe the fluid amplifiers herein as each being provided with a power fluid inlet, a pair of opposed control fluid inlets, a single fluid receiver and a pair of vent passages intermediate the control fluid inlets and the receiver.

The power fluid inlet and control fluid inlets each comprise a fluid passage in communication with a source of pressurized fluid at a first end thereof and terminating in a fluid flow restrictor or nozzle for issuing a jet therefrom at a second end thereof. Thus, the power fluid inlets of amplifiers 5 and 6 respectively comprise fluid passages 7 and 17 in communication at first ends thereof with a common source or supply of constant pressurized (power) fluid, herein identified P and terminating at second ends thereof in fluid flow restrictors (nozzles) 9 and 19 for generating constant pressurized streams or (power) jets of fluid issuing from such nozzles and directed along the centerline axes of the fluid amplifiers. The centerline axes of amplifiers 5 and 6 are defined respectively as the straight lines along which nozzle 9 and downstream fluid receiver 10, and nozzle 19 and receiver 11 are aligned. In like manner, the control fluid inlets of amplifier 5 comprise fluid passages 20 and 21 terminating respectively in opposed fluid flow restrictors 22 and 23 for generating control jets of fluid issuing therefrom and directed substantially laterally at the power jet from opposite sides thereof. The control fluid inlets of amplifier 6 comprise fluid passages 24 and 25 terminating respectively in opposed restrictors 26 and 27 for generating a second pair of control jets directed at the power jet therein. Passages 20 and 25 are in communication with a source of differentially pressurized fluid signals P -P (AP wherein the magnitude of differential pressure between the pair of signals P P represents an input signal to be amplified. The push-pull (diflierentially pressurized) input signal P 1-P 2 is of the analog type, that is, variable in magnitude of pressure generally as a function of some system parameter, Passages 21 and 24 are in communication with a common source of fluid P adjustable in pressure within a predetermined range of pressures.

The control jets issuing from nozzles 23, 26 represent a bias signal which determines an operating point On a nonlinear input-output characteristic curve of each of the fluid amplifiers in the absence of an input signal in passages 20, 25. A family of such characteristic curves for a single amplifier is illustrated in FIGURE 3 wherein the abscissa AP /P represents the ratio of differential pressure (P P or F -P in the two control fluid inlets of the single amplifier to the supply pressure of the power fluid, and the ordinate P /P represents the ratio of output pressure (pressure of fluid received in the fluid receiver) to supply pressure of the power fluid. Each curve is symmetrical about the ordinate for a amplifier geometry symmetrical about its centerline axis. Each curve is plotted for a different load R, the uppermost curve being for an infinite load R=oo corresponding to the condition of the receiver being completely blocked, and the lowermost curve for R=R 2 where R is defined as the load approximating the flow resistance of a control nozzle of an identical amplifier operating at the Same power fluid supply pressure and connected in series with the amplifier receiver. The alignment of the power nozzle and receiver is evident from the characteristic curves since at zero or balanced control fluid pressures, AP =O a maximum output pressure P is recovered in the receiver. With increased unbalance (i.e. larger differential) of the control pressures, the output pressure decreases in a nonlinear manner as illustrated. The slope of the characteristic curve represents the gain AP /AP of the amplifier, and since the slope is nonlinear, the gain is also correspondingly nonlinear. The nonlinearity is due primarily to the amplifier geometry wherein the power nozzle width, receiver width, and distance from power nozzle to receiver define the maximum pressure recovery in the receiver for each load condition. It is this nonlinear feature of this fluid amplifier which permits its use as a variable gain device. The bias signal P determines the operating point on a particular load curve, and since small (input) signal operation is assumed, the gain is determined and fixed by bias signal P The gain of each amplifier may be greater or less than unity as determined by the slope of the particular portion (about the operating point) of the selected input-output curve. Thus, the gain is greater than unity along the steeper portion of the curve and less than unity along the less steep portion. As a specific example, the gain on the load R=2R curve in the range of the operating point control pressure (i.e. the bias signal) of approximately is approximately 3.0. The pressure P of the bias control fluid can be adjusted manually or automatically (by means of a suitable valve connected between the supply and passages 21, 24) as determined by the particular fluidic circuit of which the subject device forms a part thereof. Thus, the gain of the particular fluidic circuit may be controllably varied in response to a particular magnitude or desired limit of a system parameter, or as a function of a particular system parameter. As one example, my variable gain device finds use in a fluidic jet engine control system wherein the gain in one part of the system is sensitive to engine loading and temperature eflects, and my device functions as a gain equalizer to nullify this particular gain sensitivity.

Two pair of opposed vent passages 28, 29 and 30, 31 are the final elements of my device and are located intermediate the receiver and control fluid inlets on opposite sides of the centerline axis in amplifiers 5 and 6, respectively. The terminal ends of the vent passages, designated V, are in communication with a selected medium such as the ambient atmosphere, or, in the case wherein the fluid employed is a liquid, a return passage to the sump of the pressurized fluid supply. The vent passages relieve fluid pressure adjacent the receivers in that the fluid of the power jet which does not directly impinge on the fluid receiver is directed away therefrom through the vent passages. The fluid received in fluid receivers 10 and 11 is thus a differentially pressurized push-pull output fluid signal designated P -P (AP which represent the amplified input signal AP A schematic representation of my FIGURE 1 device is illustrated in FIGURE 2 wherein the various pressurized input and output fluid signals and sources are indicated by the notation employed in FIGURE 1. The operation of my device will now be explained.

The device is assumed to be constantly supplied with a pressurized power fluid maintained at a substantially constant pressure P The bias signal offsets the power jets relative to the centerline axes of the receivers by an amount proportional to the magnitude of the pressure of the bias signal. The coaction of the bias and input signals in each amplifier causes a proportional deflection of the two power jets, relative to the offset due to bias signal P alone, whenever input signals P and P are not equal to zero. Likewise, the power jets are deflected relative to the centerline axes of the receivers whenever input signals P and P g are not equal to P Thus, the input signals P and P cause deflections of the power jets relative to their biased or offset positions. The differential pressure input signal P -P is assumed to be of magnitude sufficiently small such that small signal operation is maintained, that is, operation is along a small and therefore substantially linear portion of the selected nonlinear input-output curve. It is further assumed that both fluidic amplifiers are of identical construction and the receivers of each are in communication with identical and known loads (fluid flow restrictors) in order to obtain symmetrical push-pull operation. Nonsymmetrical push-pull operation is obtained, when desired, by employing identical amplifiers with (1) unequal receiver loads (2) unequal biases or (3) unequal power fluid supply pressures, or (4) by employing nonidentical amplifiers.

An example of the variable gain characteristics of a specific push-pull arrangement of my FIGURE 1 device is illustrated in FIGURE 4 wherein each amplifier has the input-output characterstics illustrated in FIGURE 3. The variable gain characteristics illustrated in FIGURE 4 were obtained for a power fluid supply pressure of 12 pounds per square inch gage (p.s.i.g.) and a receiver load R=R The variable gain characteristics for the pushpull device of FIGURE 1 is illustrated for five different bias pressures in FIGURE 4. The bias pressures P through P are 2.0, 2.5, 3.0, 4.0, and 5.0 p.s.i.g., respectively. The abscissa and ordinate of the FIGURE 4 graph are in terms of p.s.i. differential pressure. Thus, it can be seen that for small signal operation of approximately 11.0 p.s.i. differential pressure of the control input signal P t- 2, a controllably variable gain is obtained as a function of the bias signal pressure P This particular small signal range of operation is, of course, obtained for a fluidic device having a specific construction and the above-enumerated power fluid supply pressure and receiver load constants. For other constructions of the fluidic device, or for other power fluid supply pressures and, or loads, the small signal operating range may be less or greater than 1.0 p.s.i. The bias pressure is maintained at a value greater than the maximum differential pressure of the input signal to assure both small signal and single-quadrant operation of each amplifier. Thus, each amplifier is preferably operated in a region of the FIGURE 3 curves between the most steep slope outwardly to larger magnitudes of AP /P From the foregoing description, it can be appreciated that my invention makes available a new variable gain fluidic device which provides a controllably variable gain as a function of the pressure of a bias signal generating a jet of fluid coplanar with the power jet and control input signal jet. Gains of greater or less than unity are obtained by means of the bias signal which sets the operating point of the fluid amplifier along a more or less steep slope portion of the input-output characteristic curve of the fluid amplifier. A single fluidic amplifier comprises my device when employing only single-sided control input signals whereas a push-pull arrangement of two such amplifiers is employed for the more usual differentially pressurized control input signals employed in analog-type fluidic circuitry.

Having described a particular embodiment of my variable gain fluidic device, it is believed obvious that modification and variation of my invention is possible in light of the above teachings. Thus, the control nozzles may be disposed at angles other than 90 with respect to the power nozzle, but still being coplanar therewith, it being understood that the 90 jet intersecting relationship provides the maximum degree of jet deflection.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A two-dimensional flow, variable gain fluidic device comprising first and second interconnected fluid amplifiers of the analog type, said amplifiers of identifical construe tion and comprising first means in communication with a common source of constant pressurized fluid for generating a pair of constant pressurized first jets of fluid,

only one pair of fluid receivers downstream from said first means and coaxially aligned therewith, said receivers disposed in direct fluid communication with said first means,

two pair of vent passages on opposite sides of centerline axes determined by said first means and said receivers, said vent passages intermediate said first means and said receivers,

second means in communication with a source of variable and differential pressurized fluid for generating a pair of variable and differentially pressurized jets of fluid representing an input signal to be amplified and for controllably deflecting by momentum exchange the first jets relative to said receivers, and

third means coplanar with said first and second means for providing a controllably variable gain for said device.

2. The variable gain fluidic device set forth in claim 1 wherein said second and third means are disposed in opposing relationship in each amplifier intermediate said vent passages and said first means for controllably reflecting by momentum exchange the first jets relative to said receivers, the differential pressure of the fluid received in said receivers being a push-pull output signal representing the amplified input signal.

3. A two-dimensional flow, variable gain fluidic device comprising a first fluid amplifier of the analog type, said first fluid amplifier comprising first means for generating a constant pressurized first jet of fluid,

a first fluid receiver downstream from said first generating means and coaxially aligned with the centerline axis thereof for receiving the first fluid jet, said first receiver being the only receiver in said first amplifier and disposed in direct fluid communication with said first generating means,

first venting means intermediate said first receiver and said first generating means for relieving fluid pressure adjacent said first receiver,

second means for generating a variable pressurized second jet of fluid representing an input signal to be amplified, and

third means for generating-a pressurized third jet of fluid adjustable in pressure Within a predetermined range of pressures and independent of the input signal to be amplified, said second and third generating means disposed in opposing relationship intermediate said first venting means and said first generating means for controllably deflecting by momentum exchange the first jet relative to said first receiver, and

a second fluid amplifier of the analog type to provide push-pull operation of said device, said second fluid amplifier comprising fourth means for generating a constant pressurized fourth jet of fluid,

a second fluid receiver downstream from said fourth generating means and coaxially aligned with the centerline axis thereof for receiving the fourth fluid jet, said second receiver being the only receiver in said second amplifier and disposed in direct fluid communication with said fourth generating means,

second venting means intermediate said second receiver and said fourth generating means for relieving fluid pressure adjacent said second receiver,

fifth means for generating a variable pressurized fifth jet of fluid wherein the variable differential pressure of the second and fifth fluid jets represents a pushpull input signal to be amplified, and

sixth means for generating a pressurized sixth jet of fluid adjustable in pressure within a predetermined range of pressures and independent of the input sigr nal to be amplified, said fifth and sixth generating means disposed in opposing relationship intermediate said second venting means and said fourth generating means for controllably deflecting by momentum exchange the fourth jet relative to said second receiver, the third and sixth jets representing bias signals determining the operating points on the nonlinear input-output characteristic curves of said first and second fluid amplifiers, the gain of said first and second fluid amplifiers being a function of the bias signals and being controllably variable by adjustment of the pressurizers thereof, the differential pressure of the fluid received in said first and second receivers being the output of said device and representing the push-pull amplified input signal, the output pressure in each amplifier being maximum when the difference between the input signal pressure and the bias pressure equals zero and decreasing with increased unbalance of the input signal and bias pressures. 4. The variable gain fluidic device set forth in claim 3 wherein said first and second venting means each comprise a pair of vent passages disposed on opposite sides of the corresponding centerline axis. 5. The variable gain fluidic device set forth in claim 3 wherein said first and fourth generating means comprise first fluid passages in communication with a common source of constant pressurized fluid at first ends thereof and terminating in first and fourth fluid flow restrictors, respectively, for issuing the first and fourth jets at second ends thereof, said second and fifth means comprise second fluid passages in communication with a source of variable differential pressurized fluid representing the input signal to be amplified at first ends thereof and terminating in second and fifth fluid flow restrictors, respec tively, for issuing the second and fifth jets at second ends thereof, and said third and sixth means comprise third fluid passages in communication with a common source of pressurized fluid independent of the input signal to be amplified and adjustable in pressure at first ends thereof and terminating in third and sixth fluid flow restrictors, respectively, for issuing the third and sixth jets at second ends thereof, said second and third restrictors disposed in opposing relationship, said fifth and sixth restrictors disposed in opposing relationship. 6. The variable gain fluidic device set forth in claim 3 wherein the pressures of the fluid comprising the third and sixth jets is greater than the pressures of the fluid comprising the second and fifth jets.

7. The variable gain push-pull fluidic device set forth in claim 3 wherein said first and second fluid amplifiers are of identical construction,

said first and fourth generating means in communication with a first common source of constant pressurized fluid, and

said third and sixth generating means in communication with a second common source of pressurized fluid independent of the input signal to be amplified and adjustable in pressure within a predetermined range of pressures whereby said first and second fluid amplifiers function at the same operating point.

8. The variable gain fluidic device set forth in claim 7 wherein the pressure of the fluid comprising the third and sixth jets is greater than the maximum change in pressure of the fluid comprising the second and fifth jets to obtain small signal operation. about a particular common fluid amplifier operating point as determined by the common bias signal, the gain of said device being controllably variable as a function of the pressure of the bias signal to values greater than unity for amplifier operation along the portions of the input-output characteristic curve having a relatively steep slope, and less than unity along the portions of the curve having a less steep slope.

9. The variable gain fluidic device set forth in claim 3 wherein said first, second and third generating means are coplanar, and said fourth, fifth and sixth generating means are coplanar, and said second common source of pressurized fluid provides fluid at a constant pressure magnitude.

10. The variable gain fluidic device set forth in claim 7 wherein said first, second, third, fourth, fifth and sixth generating means are coplanar.

References Cited UNITED STATES PATENTS 3,411,520 11/1968 Boules 137--8l5 3,238,959 3/1966 Boules 13781.5 3,331,379 7/1967 Boules 137--81.5 3,410,291 11/1968 Boothe et al. 13781.5 3,080,886 3/1963 Severson 137--8l.5 3,117,593 l/l964 Somers 13781.5 XR 3,279,488 10/1966 Jones 137-8l.5 3,338,515 8/1967 Dexter 137--81.5 XR 3,340,885 9/1967 Bauer l37--81.5 3,348,562 10/1967 Ogren 13781.5 3,350,008 IO/1967 Avery 235201 SAMUEL SCOTT, Primary Examiner U.S. Cl. X.R. 235201 

